1. Field of the Inventions
The present inventions relate to a water cooling device for an outboard motor having a water-cooled casing.
2. Description of the Related Art
Watercraft can use one or more outboard motors which include a casing supportable by a hull and which have lower potions adapted to be submerged in a body of water. An internal combustion engine is supported at the upper end of the casing. An exhaust passage is formed in the casing. The exhaust passage guides exhaust gas discharged from the internal combustion engine, from the upper end of the casing toward the lower end, to be discharged in the body of water from the lower end. The intermediate section between an upstream-side passage and a downstream-side passage in the exhaust passage can be used as an expansion chamber. A cooling water passage extending along the exhaust passage is formed in the casing. The downstream end of the cooling water passage is open to the expansion chamber. Such an outboard motor is disclosed in Japanese Patent Publication No. JP-A-2003-3844.
When the internal combustion engine is driven, the watercraft is propelled. In this case, driving of the internal combustion engine allows exhaust gas discharged from the internal combustion engine to be discharged into the body of water through the exhaust passage. The exhaust gas passes through the expansion chamber in the exhaust passage to thereby reduce its exhaust noise. The casing is heated by the exhaust gas passing through the exhaust passage. When the casing is heated by the exhaust gas to a high temperature, water sticking on the external surface of the casing is evaporated by the heat. Therefore, if the water is seawater, as a result of the evaporation, the calcium content in seawater sticks on the external surface of the casing, which might cause whitening of the external surface. This whitening unfavorably lowers the quality of external appearance of the outboard motor.